The invention relates to an arrangement in a perforated roll of a fiber web machine, which arrangement includes:                a roll shell,        holes adapted through the roll shell,        a sensing system arranged in the roll shell, which sensing system includes at least one pair of leads, to which one or more sensors have been connected.        
The invention also relates to a prefabricated sensor sheet for a perforated roll of a fiber web machine.
It is known that various nip measurements are performed for example in connection with service shutdowns on fiber web machines. In these, a temporary sensing system arranged because of the measurements is arranged on the surface of a roll, the measurement is performed, and the sensing system is removed. For example the so-called E-nip measurement technology represents prior art. It can be used for measuring the cross-sectional profile of the length of the nip in static conditions, but the measurement does not directly measure the cross-sectional distribution of the nip pressure or the MD distribution of the pressure. Moreover, one known measurement is Valmet Technologies, Inc.'s iRoll portable measurement, which can be used for measuring the cross-sectional profile of the nip pressure/force by means of a sensor installed temporarily on the surface of the roll.
The arrangement of a sensing system for example in the suction roll of a fiber web machine is known from European patent publication 1 719 836 B1. The sensing system includes a pair of leads embedded in the shell of the roll, to which pair of leads one or more sensors have been connected to determine various issues in the roll. The leads of the pair of leads are taken from between through holes arranged in the roll shell to the end of the roll and from there further to a processor. In the processor, the measurement signal established by the sensors and transmitted by the pair of leads is analyzed so as to perform various measurements. The sensors have been arranged around holes, in which case the sensors have an opening for the hole. It is troublesome to take the leads of the pair of leads between the through holes, and this hence raises the manufacturing costs of the roll. Moreover, when the sensor is around the holes, it may get damaged when the through holes are drilled in the roll shell.
Attempts have been made to solve the problem related to the arrangement of the sensing system also for example so that the location of the sensing system is provided with blind drilled holes in terms of the through holes, and the rest of the roll shell is drilled in a manner defined or accepted by the end user of the roll. The angle of pitch of the sensing system with respect to the axis of the roll can be calculated so that the pitch of the drilling patterns of the blind drilled holes is constant, for example 1, 2, 3 . . . drilling patterns per shift in the circumferential direction of the drilling pattern. In this case, the number of shifts of the drill bits from one side of the sensing system to the other is always constant in the drilling stage. In this way, the goal has been to make the drilling work as easy as possible, to avoid errors in the work and to perform the work quickly. There are so many drilling patterns of blind drilled holes on top of each other in the circumferential direction of the roll that the sensing system fits completely inside the drilling patterns of blind drilled holes. FIG. 1 shows an example image of the blind drilled holes at the sensing system location of a suction roll. The rastered areas on the roll shell are blind drilled holes with a pitch of 2, and the unrastered areas are normal through holes. However, the shortcoming of this solution is the uneven perforation of through holes on the roll, because there are no through holes at the sensing system locations. Moreover, here the drilling of the through holes requires specific measures in each drilling sequence, for example in the form of the shifting of the drill bits.
The purpose of the present invention is to accomplish an arrangement in a perforated roll of a fiber web machine, as a result of which it is simpler and quicker to arrange a sensing system in a perforated roll than in prior art solutions. Another purpose of the present invention is to also accomplish a prefabricated sensor sheet for a perforated roll of a fiber web machine, by means of which prefabricated sensor sheet it is simpler and quicker to arrange a sensing system in a perforated roll of a fiber web machine.